SK hynix shares closed almost 9 percent lower at a 20-week low - the biggest one-day drop in nine months. Samsung, the world's biggest DRAM maker, tumbled 6.2 percent to a 9-week low of 1.23 million won ($1,100) - the stock's biggest daily fall in nearly four years.

"It looks like Apple doesn't want to see Samsung and hynix dominate the chip market. Apple wants to maintain its bargaining power by keeping Elpida running," said Choi Do-yeon, an analyst at LIG Investment & Securities.

U.S.-based Micron Technology Corp is in talks to acquire Elpida's business as the Japanese firm tries to restructure after tough market conditions and global competition drove it into bankruptcy protection.

"A merged Micron-Elpida could pose a significant threat to South Korean memory chipmakers, and Elpida's huge order from Apple was the spark that triggered these worries," said Lim Dol-yi, an analyst at Solomon Investment & Securities.

Samsung declined to comment, as did the Japanese court-appointed trustee handling Elpida's rehabilitation.

A spokeswoman for SK hynix said: "We are receiving more orders for mobile DRAM chips from our customers." She declined to comment on whether Apple had reduced orders from the firm.

Technology shares were also impacted by a broader sell-off after talks to form a new Greek government failed, stoking concerns the country may exit the euro zone and increase financial market uncertainty. Shares in flat-screen maker LG Display slid 4.5 percent. Hyundai Motor lost 4 percent..

"Samsung shares were already facing pressure since offshore investors began cutting back on risk during the latest streak of sell-offs, but the news surrounding Elpida was the straw that broke the camel's back," said Rhoo Yong-suk, an analyst at Hyundai Securities. "It was just unfortunate timing that coincided with jitters surrounding Greece."

(Reporting by Miyoung Kim; Additional reporting by Joonhee Yu and Hyunjoo Jin in SEOUL and Mari Saito in TOKYO; Editing by Jonathan Hopfner and Ian Geoghegan)